Diaphragm pacemakers, also known as breathing pacemakers, are typically used in patients suffering from a variety of breathing diseases such as central sleep apnea, hypoventilation, and quadriplegia. In normal breathing patterns, we draw air into our lungs, oxygenate our blood via gas exchange in the alveoli, and exhale. Our respiratory rate automatically adjusts as the carbon dioxide and oxygen content in the blood changes. Accordingly, when there is a buildup of CO2 levels in our blood and tissue, the central nervous system should automatically generate nerve signals to stimulate breathing. These nerve signals are relayed to the diaphragm and the chest wall muscles and collectively contract to expand the lungs. However, in individuals suffering from breathing diseases such as the diseases identified above, there is a breakdown in this respiratory process and the nerve signals are not properly generated or are of an insufficient magnitude to stimulate the breathing. Accordingly, diaphragm pacemakers provide an artificial means of inducing respiration.
Diaphragm pacemakers are implantable medical devices that stimulate the phrenic nerves in order to cause the contraction of the diaphragm in patients suffering from breathing diseases. In a basic system, a diaphragm pacemaker consists of a surgically implanted receiver and electrodes and an external transmitter that is connected to an antenna also worn outside the body. The external transmitter and antenna send radiofrequency energy to the implanted receiver. The receiver then converts the radio waves into stimulating pulses that are sent down the electrodes to the phrenic nerves causing the diaphragm to contract resulting in inhalation of air. When the pulses stop, the diaphragm relaxes and exhalation occurs. Repetition of this pattern produces a normal breathing pattern.
In traditional diaphragm pacemakers, the rate and duration of the pulses, which represent the respiratory rate and depth of inhalation, are fixed and do not vary with the ever changing physiological requirements of the body. To adjust the settings, a patient can be hooked up to a data transmitter to provide diagnostic monitoring of the diaphragm pacing equipment as well as the patient's physiological response to the stimulation. The data transmitter records and transmits the data so that a medical professional can determine whether the settings of the diaphragm pacemaker need to be adjusted.
It is also possible to control the pacing of the system using a pulse oximeter. A pulse oximeter is a medical device that indirectly measures the oxygen saturation of a patient's blood (as opposed to measuring oxygen saturation directly through a blood sample) and changes in blood volume in the skin, producing a photoplethysmograph (PPG). However, the use of pulse oximeters has its disadvantages, such as a patient could have excellent blood oxygen levels while still suffering from respiratory acidosis due to excessive carbon dioxide. Thus, it is necessary to also measure CO2 levels.
Accordingly, it is desirable to provide for a more accurate and suitable manner in which to monitor and adjust the settings of a diaphragmatic pacemaker.